The universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from the global system for mobile communications system (GSM), which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access (W-CDMA) technologies.
FIG. 1 shows an exemplary diagram illustrating an Universal Mobile Telecommunication System (UMTS) network of a conventional mobile communication system. The UMTS is comprised of, largely, a user equipment (UE) or a mobile terminal (referred to a terminal hereafter), a UMTS Terrestrial Radio Access Network (UTRAN), and a core network (CN). The UTRAN comprises at least one Radio Network Sub-system (RNS), and each RNS is comprised of one Radio Network Controller (RNC) and at least one base station (Node B) which is controlled by the RNC. For each Node B, there is at least one cell.
FIG. 2 is an exemplary diagram illustrating a structure of a Radio Interface Protocol (RIP) between a UE and the UTRAN. Here, the UE is associated with a 3rd Generation Partnership Project (3GPP) wireless access network standard. The structure of the RIP is comprised of a physical layer, a data link layer, and a network layer on the horizontal layers. On the vertical plane, the structure of the RIP is comprised of a user plane, which is used for transmitting data, and a control plane, which is used for transmitting control signals. The protocol layers of FIG. 2 can be categorized as L1 (first layer), L2 (second layer), and L3 (third layer) based on an Open System Interconnection (OSI) model. Each layer will be described in more detail as follows.
The first layer (L1), namely, the physical layer, provides an upper layer with an information transfer service using a physical channel. The physical layer is connected to an upper layer called a medium access control (MAC) layer through a transport channel. Data is transferred between the MAC layer and the physical layer through the transport channel. Data is also transferred between different physical layers, i.e. between physical layers of a transmitting side and a receiving side, through the physical channel.
The MAC layer of the second layer (L2) provides an upper layer called a radio link control (RLC) layer with a service through a logical channel. The RLC layer of the second layer supports reliable data transfer and performs segmentation and concatenation of a service data unit (SDU) received from an upper layer.
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane, and handles the controlling of transport channels and physical channels with respect to the establishment, re-configuration, and release of radio bearers (RB). The RB refers to a service provided by the second layer (L2) for transferring data between a UE and the UTRAN. In general, an RB being established refers to providing the characteristics of the protocol layers and channels required in providing a particular service, and refers to the procedures of configuring each particular parameter and operating method.
When the RRC layer of a particular UE and the RRC layer of the UTRAN are connected to allow messages to be transferred therebetween, that particular UE is said to be in RRC connected state, while the UE is said to be in idle state when there is no connection. A UE in RRC connected state is further divided into a URA_PCH state, a CELL_PCH state, a CELL_FACH state, and a CELL_DCH state. For those UEs in idle state, in URA PCH state, or in CELL_PCH state, a discontinuous reception (DRX) method is employed to minimize power consumption by discontinuously receiving a SCCPCH (Secondary Common Control Physical Channel) to which a PICH (Paging Indicator Channel) and a PCH (Paging Channel) are mapped. During the time periods other than for receiving the PICH or the SCCPCH, the UE is in sleeping mode state.
In the related art, the UE performing the DRX (discontinuous reception) method wakes up at every CN domain specific DRX cycle length or UTRAN specific DRX cycle length to receive a UE specific paging indicator (PI) of the PICH. The related art UE specific PI is used in order to notify a particular UE that a paging message for the particular UE will be transmitted via the PCH.
The PICH is divided into PICH frames having a length of 10 ms, and a single PICH frame is comprised of 300 bits. The 288 bits in the front portion of the PICH frame are used for the UE specific PICH, and more than one UE specific PI are transmitted. The 12 bits at the end of the PICH frame are not transmitted. For convenience, the 288-bit front portion of the PICH is defined as the “UE PICH,” while the 12-bit rear portion is defined as the “PICH Unused Part.”
A RRC connection will be described in more detail as follows. In order to establish the RRC connection with the UTRAN, an idle state of terminal has to perform a RRC connection procedure. FIG. 3 shows an exemplary diagram for explaining how a RRC connection is established. As illustrated in FIG. 3, to establish the RRC connection, the terminal transmits a RRC Connection Request Message to the UTRAN, and then the UTRAN transmits a RRC Connection Setup Message to the terminal in response to the RRC Connection Request Message. After receiving the RRC Connection Setup Message by the terminal, the terminal transmits a RRC Connection Setup Complete Message to the UTRAN. If the above steps are successfully completed, the terminal establishes the RRC connection with the UTRAN.
In the related art, if a terminal, which is in the CELL-PCH state, transmits an uplink ARQ (Automatic Repeat Request) or HARQ (Hybrid ARQ) feedback in response to the received downlink data, the terminal always performs a CELL UPDATE procedure so that the ARQ or HARQ feedback is transmitted from the terminal to the UTRAN in the CELL_FACH state. Due to this circumstance, the terminal has to perform the CELL UPDATE procedure to transit its state into the CELL_FACH state even if the terminal rarely receives downlink data. This would causes a great drawbacks of wasting radio resources and delaying of transmission time, as the terminal transits its state more than necessary.